The naming conventions GRUB uses for hard disks and partitions differ from those used for normal Linux devices. It more closely resembles the simple disk enumeration the BIOS does and the syntax is similar to that used in some BSD derivatives. In GRUB, the numbering of the partitions starts with zero. This means that (hd0,0) is the first partition of the first hard disk. On a common desktop machine with a hard disk connected as primary master, the corresponding Linux device name is /dev/sda1.

The four possible primary partitions are assigned the partition numbers 0 to 3. The logical partitions are numbered from 4:

Being dependent on BIOS devices, GRUB does not distinguish between IDE, SATA, SCSI, and hardware RAID devices. All hard disks recognized by the BIOS or other controllers are numbered according to the boot sequence preset in the BIOS.

Unfortunately, it is often not possible to map the Linux device names to BIOS device names exactly. It generates this mapping with the help of an algorithm and saves it to the filedevice.map, which can be edited if necessary.